Ultrasonic transceiver

ABSTRACT

Simplified ultrasonic transceiving apparatus preferably incorporating transducer means coupling ultrasonic vibrations into a medium, said means being bidirectional in operation to also convert vibrations from the medium into electrical signals; an oscillatory signal applied to said transducer means for propagation into the medium, and means forming an output signal combining the oscillatory signal and vibrations received from within the medium into an electrical signal.

1221 Filed United States atent 21 Appl. No.

[45] Patented [73] Assignee Primary Examiner-Richard A. Farley ABSTRACT:Simplified ultrasonic transceiving apparatus preferably incorporatingtransducer means coupling ul- [54] TBANSCEIVER trasonic vibrations intoa medium, said means being rawmg Figs bidirectional in operation to alsoconvert vibrations from the [52] US. 340/1, medium into electricalsignals; an oscillatory signal applied to' 340/3, 73/194 said transducermeans for propagation into the medium, and [51] lntJ G0ls 9/66 meansfonning an output signal combining the oscillatory [50] Field of Search340/3, 3 D, signal and vibrations received from within the medium intoan 1; 73/ 1 94 A electrical signal.

48 a 63 J V L4: G6 75 1,, i 7 .s/amu t a 'J- 4 .1- our/ 07 l I'/ 68 t L54- z 53 as 1 c? 5/ ULTRASONIC TRANSCEIVER This application is acontinuation of Ser. No. 672,091, filed Oct. 2, I967, now abandoned andis related to application Ser. No. 672,092, filed Oct. 2, 1967 which wasissued as Pat. No. 3,431,551.

SUMMARY OF PROBLEM AND INVENTION Ultrasonic apparatus is traditionallyused for obtaining graphic representations of the interiors of opaqueobjects in fields such as materials inspection, physiological analysisand the like. Devices in the prior art include extensive and complexequipment with traditionally separate transmitters and receivers withtypically complex multiplexing or transducer switching apparatus. With aview of obtaining velocity information, it will be appreciated thatcoupling transmitter and receiver to a transducer or other radiatingelement yields a rather complex system for obtain doppler shiftinformation.

Doppler shift information is particularly useful in evaluating flowvelocities, internal vibrations, and other information associated withrelative movements which give rise to doppler shift in the reflectedwave front. Therefore, this invention is summarized as providing a newand improved ultrasonic transceiver, and more particularly, anultrasonic transceiver providing doppler shift information whereinsimultaneous transmission and reception of reflected waves provides anoutput signal from a simplified device.

An object of the present invention is to provide a new and improvedcontinuous wave or pulsed transmitting and receiving means forultrasonic uses which avoids the requirements of timing circuits and thelike.

Another object of the present invention is to provide a new and improvedtransceiver which emits and receives ultrasonic radiation from atransducer without multiplexing or switching of the transmitter andreceiver between radiating elements.

Yet another object of the present invention is to provide a new andimproved continuous wave ultrasonic transceiver wherein the transmittingfrequency remains stable while signals returned from the mediumindicative of doppler shift are amplified and mixed with the transmittedfrequency.

Still another object of the present invention is to provide a new andimproved continuous wave device wherein the doppler shift information ismodulated in the tank of the transmitting device without effectingtransmission.

One object of the present invention is to provide a new and improvedtransceiver apparatus having only one active element, and that elementcooperates with the oscillator, doppler shift demodulator and amplifier.

Another object of the present invention is to provide a new and improvedtransceiver oscillator operating sufficiently near Class Acharacteristics to amplify and yet which is sufficiently nonlinear tomodulate the oscillator signal with the doppler shift signalinformation.

Other objects and advantages of the present invention will become morereadily apparent from a consideration of the included specification anddrawings wherein:

FIG. 1 is a schematic wiring diagram of the preferred embodiment of thepresent invention; and,

FIG. 2 is a schematic wiring diagram of an alternative embodimentproviding additional internal amplification.

Attention is first directed to FIG. 1 of the drawings which indicatesthe transceiver of the present invention with the numeral 10. Thetransceiver incorporates a transducer means 12 for radiating andcoupling ultrasonic wave fronts into a medium. For present purposes, amedium is an opaque material having relatively moving internalcomponents. By way of example, reference is made to pipes having fluidflow therein wherein the flowing fluid causes a shift in frequency ofreflected wave fronts returned to the transducer 12. Also, reference ismade to physiological systems wherein relative movement is related tothe vital signs of patients during examination. Those skilled in theultrasonic arts are familiar with various coupling techniques used withthe transducer means 12. For instance, the means 12 may typically be apiezoelectric crystal which is placed flat against the surface of themedium and coupled thereto by wetting the surface to mechanically couplevibrations from the means 12 into the medium. Because of generic natureof the medium, it has been omitted from the drawings and symbolicrepresentation of the transducer means 12 is sufficient for purposes ofthe present invention.

Since several circuit functions are achieved in the preferred embodiment10 of the present invention, attention is first directed to theindividual circuit elements which will be noted and the circuitfunctions of the apparatus will be described in greater detailhereinafter. Attention is first directed to a tunable, tapped inductor14. The transducer means 12 incorporates sufficient tuning capacitancewhich is connected across the inductor 14 through the parallelcombination of the resistor 15 and capacitor 16. The inductor 14 istapped at a point selected for proper operation (midpoint in manycases), and the tapped signal is provided through a series capacitor 17and adjustable resistor 18 to the emitter of a bipolar or monopolar(FET)-type transistor 20. The transistor emitter (or drain in themonopolar transistor) is communicated with ground by means of a seriesresistor 21. The tank circuit including the inductor 14 is maintained ata selected bias voltage by means of a series resistor 23 communicatedwith the DC power source. The collector (or source in the monopolartransistor) circuit of the transistor 20 incorporates a series loadresistor 24, which is bypassed by a capacitor 25. The output of thecircuit means 10 is obtained from the collector by means of a seriescoupling capacitor 26.

Attention is next directed to the fact that the circuit shown in FIG. 1incorporates a tank circuit including the inductor l4 and thecapacitance of the transducer means 12. The upper end of the tank isconnected to the base (or gate of the monopolar transistor) of thetransistor 20, and the tap on the inductor 14 communicates through thelevel setting resistor 18 to the emitter of the transistor 20. Theadjustable signal from the resistor 18 provided to the active circuitelement 20 controls the level of oscillations in the tank circuit. Whilethe tank cooperates with the active element means 20 to serve as signalgenerating means for the present invention, it will be noted that afurther function is accomplished by the tank circuit. Reference is madeto the fact that the transducer means 12 is not only a circuit elementcomprising a portion of the oscillator, but also, the transducer means12 is also a signal source for injecting doppler shift signals into thetank.

Consider response of the transducer means 12 to doppler shift signals.The signal wave front is radiated from the transducer means 12 into themedium and is returned as reflections from interfaces found in themedium. With no relative velocity, the signal returned is the frequencytransmitted and differs only by providing a phase shift in the signal.This phase shift between the transmitted and received Waves will cause ashift in the level of oscillation and therefore a change in the DCcurrent in the transistor 20. In this invention, this DC phase shift isnot used in the output shown. However, relative movement within themedium provides the doppler shift (a shift in frequency) signal in theoscillator means presently described.

On return of the wave front at a different frequency, the beat frequencyin the tank circuit modulates the tank circuit signal applied to thebase of the transistor 20. In this regard, it will be noted that themodulation is amplitude modulation whereby the oscillator signalenvelope carries the doppler shift information. Thus it will be notedthat mixer circuit means cooperates with the transistor to amplify themodulated envelope for output through coupling capacitor 26.

In the transceiver 10, the signal generating means operates continuouslyand indefinitely. And, the transceiver 10 functions without multiplexingapparatus, multiple antennas or timing circuits. That is to say, thetransducer 12 is simultanemedium. In the mixing of transmitted andreceived signals, it

will be noted that the oscillator is marginally operated by feedbackcontrol through the variable resistance 18, whereby oscillations areonly weakly maintained. The marginally stable condition of theoscillator at the marginal operational point makes the device moresensitive to receive signals providing a relatively good receiver whileyet maintaining transmitter stability. More specifically, operation at amarginal point of the oscillator means increases the sensitivity of thedevice by providing a large beat signal with an incremental signal atthe transducer means 12.

The transceiver is provided with a frequency responsive load acrosswhich the output signal is developed. Reference is made to the tendencyof the capacitor 25 to shunt high frequency signals to'ground. This aidsthe device in materially reducing the transmitter frequency while thedoppler shift signal is substantially amplified.

It should be noted that the transducer means 12 has a selfresonantfrequency; preferably, to give broad frequency coverage, the tank of thetransceiver 10 is operated at a frequency other than the self-resonantfrequency of the transducer means 12. When the transducer is operated atits selfresonant frequency, additional sensitivity is gained.

Attention is next directed to FIG. 2 of the drawings which illustrates aslightly more elaborate transceiver means 48. The circuitry shown inFIG. 2 varies, in the main, by including additional amplifier means aswill be noted. Considering first the details of the device, thetransducer means 50 forms a tank circuit cooperating with the inductor51. The upper end of the inductor 51 is communicated with the base of atransistor 52 (again, it may be a bipolar or monopolar transistor)having its emitter resistor 53 grounded. The inductor 51 is tapped bymeans of a coupling capacitor 54 communicating with the emitter of thetransistor 52 to complete the feedback path needed to maintainoscillations. The lower end of the inductor 51 is not directly groundedbut is connected to a bias resistor 56 and grounded through a capacitor73. The voltage level in the variable resistor 56 is obtained from apotential source 57.

The transistor 52 includes a collector load impedance 60 across whichthe amplified signal is developed. The output is taken from thecollector by means of a series capacitor 61, and high frequency signalsare shunted to ground by means of a capacitor 62. Coupling capacitor 61communicates with a voltage divider including resistors 63 and 65 whichprovide the base voltage for a transistor 64 (also, a bipolar ormonopolar transistor will serve well). The transistor 64 includes acollector load resistor 66 and an emitter bias supply including parallelelements 67 and 68. The output signal is provided through a couplingcapacitor 69 at amplified levels.

The improved transceiver means 48 shown in FIG. 2 further includes anoff-on switch 72 which regulates the voltage level for variable resistor56 and the power source for the transistors.

FIG. 2 also includes a series coupling capacitor 74 communicating withan antenna 75. The antenna is represented generically since thoseskilled in the art are familiar with details of construction andoperation for transmitting an AM signal. The antenna radiates themodulated radio frequency signal across the tank circuit and in thismanner the doppler shift signal is telemetered to a remote location.

Considering operation of the circuit shown in FIG. 2, it should be firstnoted that the tank circuit is slightly different from the one shown inFIG. 1. This is not critical since a large variety of tank circuits areknown in the art and the variation is only indicative of circuitsavailable. The tank circuit serves as the signal generating means incooperation with the active circuit element 52 whereby the signal to betransmitted is provided to the transducer means 50. The continuous waveradiation from the transducer means 50 enters the medium in a knownmanner and is reflected therein to return to the transducer means 50.Again, absent relative movement in the medium, the frequency transmittedis also the frequency returned, and therefore, no additional signal isinduced in the tank for mixing with the oscillator frequency. However,on occurrence of relative movement, the doppler shift component is notedin the transducer means 50. The returned signal is beat against thesignal from the signal generating means and the beat signal amplitudemodulates the transmittal frequency for amplification by the transistormeans 52. The amplified and modulated signal noted at the collector ofthe transistor 52 is developed across the transistor load impedance 60for coupling to the next stage. However, it should be noted that highfrequency components are filtered to ground by the capacitor means 62.The envelope is detected in the modulated signal and communicated to theamplifier stage including transistor means 64. The coupling capacitor 61is a rather large capacitance since low, audio frequencies are likely tobe passed to the transistor 64.

The amplifier means 64 functions in a conventional manner wherein thebias voltage between the base and emitter is determined by the voltagedivider including resistors 63 and 65 and the emitter circuit includingelements 67 and 68. The output signal is developed across collector loadresistor 66 and the coupling capacitor 69 communicates it with theoutput terminal.

Considering FIG. 2, it should be noted that it is similar to FIG. 1 inproviding a continuous wave ultrasonic transceiver cooperating with thetransducer means to transmit sound vibrations therefrom and to outputdoppler shift signals in an easily handled form. Moreover, the circuitryshown in FIG. 2 is adapted for telemetry to remote locations by use ofthe antenna means 75.

The circuit means 48 shown in FIG. 2 provides an amplified signal leveladequate for recording, analysis, conversion in an appropriate device,and the like.

Briefly, the foregoing described preferred embodiments of a new andimproved transceiver means; and a scope of the present invention isdefined by the appended claims.

We claim:

1. An ultrasonic transceiver comprising:

a. a transistor having base, collector, and emitter terminals;

b. a tank circuit connected to at least two of the terminals of saidtransistor for forming an oscillator circuit capable of sustainingoscillations;

c. transducer means connected in said tank circuit, said transducerhaving an impedance which at least partially comprises a portion of saidtank circuit, and being further communicated with an ultrasonic mediumfor transmitting and receiving ultrasonic vibrations;

d. said transducer means being connected to apply the signal thereacrossat least directly to said transistor for amplification; and,

e. an output circuit connected to at least one terminal of saidtransistor and provided with the amplified transducer means signal forforming an output of doppler frequency shifts representative of relativemovement in the medium.

2. The invention of claim 1 wherein said transistor is connected at itscollector to a load resistor across which the amplified signal isdeveloped, and wherein said output circuit includes a coupling capacitorconnected to said load resistor.

3. The invention of claim 1 wherein a coupling capacitor is connected tosaid transistor for deriving the the amplified signal therefrom, saidoutput circuit including:

a. a second transistor having base, collector and emitter terminals;

b. said coupling capacitor connected to one of the terminals of saidsecond transistor; and,

c. additional circuit elements connected to said second transistor forforming an amplified signal.

4. The invention of claim 3 wherein said additional circuit elementsinclude an output coupling capacitor connected to said secondtransistor.

5. The invention of claim 1 wherein said transducer means includes acapacitive impedance and said tank circuit includes an inductivereactance which forms a resonant circuit with said transducer means.

A'Mlwn tutu

1. An ultrasonic transceiver comprising: a. a transistor having base,collector, and emitter terminals; b. a tank circuit connected to atleast two of tHe terminals of said transistor for forming an oscillatorcircuit capable of sustaining oscillations; c. transducer meansconnected in said tank circuit, said transducer having an impedancewhich at least partially comprises a portion of said tank circuit, andbeing further communicated with an ultrasonic medium for transmittingand receiving ultrasonic vibrations; d. said transducer means beingconnected to apply the signal thereacross at least directly to saidtransistor for amplification; and, e. an output circuit connected to atleast one terminal of said transistor and provided with the amplifiedtransducer means signal for forming an output of doppler frequencyshifts representative of relative movement in the medium.
 2. Theinvention of claim 1 wherein said transistor is connected at itscollector to a load resistor across which the amplified signal isdeveloped, and wherein said output circuit includes a coupling capacitorconnected to said load resistor.
 3. The invention of claim 1 wherein acoupling capacitor is connected to said transistor for deriving the theamplified signal therefrom, said output circuit including: a. a secondtransistor having base, collector and emitter terminals; b. saidcoupling capacitor connected to one of the terminals of said secondtransistor; and, c. additional circuit elements connected to said secondtransistor for forming an amplified signal.
 4. The invention of claim 3wherein said additional circuit elements include an output couplingcapacitor connected to said second transistor.
 5. The invention of claim1 wherein said transducer means includes a capacitive impedance and saidtank circuit includes an inductive reactance which forms a resonantcircuit with said transducer means.